Mac1700/turntable issue

Mike35

New Member
I just purchased a VPI Prime Scout and had it installed/connected to my Mac1700 by the dealer at my office. When playing it, it sounds great, particularly compared to my old Sanyo, but when I change albums I can hear a "hum" coming out of my speakers and wonder if it is impacting my playback. I am using the VPI cable that they recommend and using a Ortofon Blue cartridge.

I have done many things as suggested by the dealer and have not resolved the issue and we have it narrowed down to two things, one of which I am hoping this group can answer. He thinks because the Mac has a two pronged outlet that this has created the noise and a three prong would solve it. Has anyone experienced this with vintage stuff?

It definitely seems to be grounding issue as if I touch the bolt that holds the tone arm in and the base, I can make it go away. If anyone has experienced this with their vintage stuff, I would appreciate your input.

thanks,
Mike
 
I have definitely grounded between the turntable and the receiver. I just ordered a wire that has an alligator clip to attach to the receiver and then has a plug to go in the outlet. It is supposed to arrive on Wednesday and I will post results. I am hoping this gets rid of the buzz!
 
Does the 1700 have a polarized AC plug? If not, reverse the connection. Same goes for the Turntable. Do one at a time till you get the best results.
 
Before you start fussing with the AC ground and it's inherent dangers .......it would seem that the ground of the cartridge/tonearm is not bonded to the table and then to the receiver. You seem to be applying a ground when you touch it.

What does a jumper from the receiver ground screw to the tone arm base do? I do not know if the scout arm grounds or bonds the wand/cartridge via a actual wire to the multi connection for the turntable ground or relies on the arm bearings to make that connection....that VPI or your dealer should know.
 
Before you start fussing with the AC ground and it's inherent dangers .......it would seem that the ground of the cartridge/tonearm is not bonded to the table and then to the receiver. You seem to be applying a ground when you touch it.

What does a jumper from the receiver ground screw to the tone arm base do? I do not know if the scout arm grounds or bonds the wand/cartridge via a actual wire to the multi connection for the turntable ground or relies on the arm bearings to make that connection....that VPI or your dealer should know.

I will try to run a ground between the two and see what happens. It was my dealer who feels certain it is my receiver and suggested the connection between the post and the AC outlet. I feel like your idea is a good one, but he didn't think it was related to the turntable or cartridge.
 
Does the 1700 have a polarized AC plug? If not, reverse the connection. Same goes for the Turntable. Do one at a time till you get the best results.


It is not a polarized connection. I have changed all the connections in all of the various configurations and still get a hum. Thanks for the input!
 
VMS type of cartridge designs have always been more susceptible to picking up noise than say the popular moving magnet designs.

The magnetic field created around the fixed coils is just more susceptible to outside influence compared to the relatively shielded magnet inside the coils of a moving magnet type cartridge.

Your capacitive, magnetic personality affecting the "hum" as you touch the arm mount, makes me suspect a cartridge shielding issue.
 
It is not a polarized connection. I have changed all the connections in all of the various configurations and still get a hum. Thanks for the input!
You don't have to use a turntable ground wire, we use them when needed and sometimes they cause more issues. so try it without it connected and store it away from other wires.

The same goes for grounding the receiver with or without.

I would start with none of your add on grounding, remove it all. Try the table without it's ground wire, and then with it, what sounds better? And to tell the truth I would not ground the receiver at all in your environment.
 
Grounding may be the popular term but really you are extending the shield from the high gain phono stage to the cartridge. Some tables do this via the cables shield, most tie a wire from the common shield tie point to the receiver chassis. Connecting to the AC would involve bonding the table motor system to earth ground of your homes electrical system, a whole 'nother can of worms.
 
You don't have to use a turntable ground wire, we use them when needed and sometimes they cause more issues. so try it without it connected and store it away from other wires.

The same goes for grounding the receiver with or without.

I would start with none of your add on grounding, remove it all. Try the table without it's ground wire, and then with it, what sounds better? And to tell the truth I would not ground the receiver at all in your environment.

So I have tried it with and without the ground and it was worse without it. I am using the VPI cable that has the ground in with the cables so I can't separate it easily. I think I will just try some plain cables without a ground and see what happens.

Why would you not ground the receiver? Is it just opening a new can of worms?

Thanks so much for you input!
 
I had the same problem with a VPI TNT and emailed VPI. They had me run a ground wire from the ground of TT(same post that runs to receiver) to the TT body (I ran it to the spindle housing under table) . It took care of my problem.
 
So I have tried it with and without the ground and it was worse without it. I am using the VPI cable that has the ground in with the cables so I can't separate it easily. I think I will just try some plain cables without a ground and see what happens.

That would almost definitely be a step backwards. Suggest using regular cables in addition to the ground wire. I've noticed certain older McIntosh models don't seem to do well where grounding is supposed to established through the signal cables.
 
The rods your electrician drove in the ground, and water pipe your electrician attached your service to establishes the ground of your electrical system. When you attach a plug with three prongs you are bonding the chassis to the service.

Adding a bonded AC cord to a vintage unit not designed to be bonded will most often introduce potentials, that is minute voltage differences, that will cause more noise.

I assume you just bought the table and/or cartridge and your dealer is grasping at straws. Back in the day, I would have tried a different cartridge already to eliminate that possible source of the problem.

I restore vintage Mac units all the time....a MAC1700 is decade beyond needing a complete restoration...THAT SAID,

I assume your previous table did not hum, just did not have the frequency response and detail a new cartridge should have. Hard to blame a receiver for a probable turntable/cartridge issue.
 
I had the same problem with a VPI TNT and emailed VPI. They had me run a ground wire from the ground of TT(same post that runs to receiver) to the TT body (I ran it to the spindle housing under table) . It took care of my problem.

How did you attach it to the spindle housing?
 
The rods your electrician drove in the ground, and water pipe your electrician attached your service to establishes the ground of your electrical system. When you attach a plug with three prongs you are bonding the chassis to the service.

Adding a bonded AC cord to a vintage unit not designed to be bonded will most often introduce potentials, that is minute voltage differences, that will cause more noise.

I assume you just bought the table and/or cartridge and your dealer is grasping at straws. Back in the day, I would have tried a different cartridge already to eliminate that possible source of the problem.

I restore vintage Mac units all the time....a MAC1700 is decade beyond needing a complete restoration...THAT SAID,

I assume your previous table did not hum, just did not have the frequency response and detail a new cartridge should have. Hard to blame a receiver for a probable turntable/cartridge issue.


The previous turntable didn't have any issues with hum.

My MAC1700 has been gone through and had much replaced by my local vintage stereo repair guy who is a long time McIntosh user.

I plan to try to run a wire like rocknroll1 suggested.

Thank you all for your help!
 
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